Field of the Invention
The present invention relates to a plant and a process for the production of helium.
The invention relates more particularly to a plant for the production of liquid helium comprising a refrigeration/liquefaction device, the refrigeration/liquefaction device comprising a working circuit in which a working fluid enriched in helium is subjected to a thermodynamic cycle in order to produce liquid helium, the circuit comprising at least one means for compressing the working fluid and several heat exchangers in order to cool/reheat the fluid to predetermined temperature levels during the cycle, the plant comprising several pipes for recovery of fluid having respective upstream ends intended to be selectively joined to respective tanks in order to transfer fluid from the tanks to the refrigeration/liquefaction device, the plant comprising a first collecting pipe having an upstream end connected to the recovery pipes and a downstream end connected to a receiving means capable of feeding the working circuit with working fluid.
The invention relates in particular to the production and distribution of liquid helium. Helium, a noble gas, is generally obtained from natural gas in plants where natural gas is purified (enriched in helium) and then liquefied in a refrigerating and/or liquefying device.
Related Art
The distribution of helium generally requires cooling of the helium to a temperature of below 4.5K (liquid state) and then its transportation and its distribution in mobile tanks, for example on semitrailers. These tanks, which can be isolated with nitrogen, generally have to be maintained at a temperature not exceeding 50 to 60K. For this reason, it is not recommended to completely empty these tanks of their helium.
In practice, after delivery, these “emptied” tanks return to the filling points at temperatures of the order of 150K and more. Thus, when the tank returns after delivery from the client and before filling it with helium, it is necessary to cool it to 4.5K as, if not, the liquid helium introduced would evaporate.
Generally, the contents remaining in these tanks are reinjected into the helium production plant in order to prevent losses of this expensive gas.
The tanks are usually cooled in the filling points by circulating (in a loop) helium from the point through the tank to be cooled in order thus to lower the temperature thereof.
Due to the potential evaporations, it is sometimes necessary to purify this gas and to reliquify it.
This recovery of relatively warm gas, its possible purification and its liquefaction require the consumption of a great deal of energy.
In addition, the gaseous helium possibly produced during the cooling may exceed the capacity of the helium liquefaction plants with which the plant is equipped.
For some helium liquefiers and/or refrigerators, the “warm” gases returned from the tanks (that is to say, at a temperature greater than the liquid nominal production temperature) are sent to the refrigerator/liquefier at different levels in the refrigerator/liquefier. For example, these recovered warm gases are reinjected at predetermined places in the working circuit of the refrigeration/liquefaction device between the “cold” and “warm” ends, that is to say at predetermined temperature levels of the helium in the working circuit.
Furthermore, when the fluid present in the tanks exhibits a high content of impurities, it is necessary to purify it beforehand in the recovery and purification system of the plant.
Thus, the fluid from the different tanks is either sent into the recovery and purification system of the plant (when it exhibits impurities) or is collected in a common collector before being injected into the working circuit of the liquefier/refrigerator (when the fluid is relatively pure). This mixture of pure fluids collected in the various tanks concerned is sent into the working circuit at a pressure/temperature level corresponding to the temperature level of the mixture of fluids.
These known processes require the consumption of a great deal of energy in order to provide for the production of liquid helium while recovering the more or less warm fluids originating from the empty tanks.